Multi-phase fluids comprise both gas and liquid components and an example would be a well stream extracted from an onshore or subsea well which comprises a mixture of gas and oil. Such a mixture can vary substantially as regards its gas and liquid components. It may comprise slugs of substantially unmixed liquid separated by primarily gaseous portions, as well as portions that are more or less homogeneous. This inconsistency of the nature of the extracted material makes it difficult to handle, in particular by pumping equipment, which can more efficiently and reliably deal with a homogeneous mixture.
Apparatus for homogenizing multi-phase fluids is known from EP-A-0379319 and WO 90/13859 in which a multi-phase fluid is supplied to a reservoir in which it tends to separate into a body of predominantly gaseous phase fluid adjacent to a pool of predominantly liquid phase fluid. The liquid phase flows out of the reservoir via an outlet conduit and a pipe channels gaseous phase fluid through the liquid phase to the outlet. A venturi restriction in the outlet conduit creates suction to draw the gaseous phase into the liquid phase flow at the outlet. Perforations along the length of the pipe draw liquid phase into the gaseous phase and aid the homogenization process.
A problem with these known multi-phase fluid homogenizers occurs when the unprocessed well stream contains sand particles or other solids. The apparatus must then be designed with large flow areas to avoid solids accumulating in narrow sections and blocking the flow or clogging the apparatus. Such accumulation seriously reduces the efficiency of the known apparatus and can prevent it working altogether.
In these known homogenizers, the relative proportions of gas to liquid in the mixture, i.e. the gas volume fraction (GVF) is directly correlated to the level of the liquid in the reservoir, in that the higher the GVF, the lower the liquid level. This relationship determines the optimum operating envelope of the apparatus. The apparatus can be adapted by choosing appropriate flow areas for respective liquid and gas streams in the outlet, combined with appropriate numbers and sizes of perforations in the pipe. For high GVF applications the liquid outflow rate, and hence the cross-sectional area of the outlet conduit, needs to be small and the perforations in the pipe reduced in size or number or both. However if the liquid flow area is made too small it becomes more prone to blockage from solids. Thus there is a practical limit, dependent upon the size and amount of the solid particles in the flow, below which the liquid flow area cannot be reduced without seriously prejudicing the performance of the apparatus. A typical lower limit in gas and oil applications for a liquid flow clearance is about 5 mm and this equates, using a perforated pipe of around 5-30 cm diameter, to a maximum GVF of 90-98% corresponding to a maximum GLR of 10-50. As a result, it is generally difficult to design the known homogenizing apparatus for optimum operation of GLR above 10-50. This is illustrated in FIG. 2.
Multi-phase mixtures with a very high gas volume fraction (GVF) are known as condensate or “Wet Gas”—a geological term for a gaseous mixture of hydrocarbons that contain a significant amount of compounds with molecular weights heavier than methane. Such wet gas fluids typically have a GVF of above approximately 95% corresponding to a gas liquid ratio (GLR) above 20. Typically such fluids also contain other non-hydrocarbon compounds such as carbon dioxide, hydrogen sulphide, nitrogen, oxygen and water.
It would be advantageous to provide apparatus which can efficiently handle high GVF multi-fluid flows, such as Wet Gas flows, without being prone to blockage from solid particles in the flow.